AccessibilityEvent/AccessibilityNodeInfo class name property should be set to...

AccessibilityEvent/AccessibilityNodeInfo class name property should be set to only framework classes.

AccessibilityEvent and AccessibilityNodeInfo have a property className which is set to the source
Java class. This is problematic since leads to leaking private classes which would allow an
accessibility service to load classes from other packages. This is strongly undesirable since
not trusted code can be loaded, and hence executed, in the accessibility service. To address
that the class name is set to the most concrete framework class extended by the info/event
source.

bug:5878943

Change-Id: I7b3114ece8772ea2773f5151e21b8a6f2006882a